Inside Science News Service

A collection of brief stories from the world of science

August 22, 2008
By Phil Schewe
Inside Science News Service

African Tree Rings Provide Climate History
Climate scientists look for evidence of historical conditions wherever they can. Annual growth rings in conifer trees in Algeria and Tunisia, for example, deliver centuries’ worth of data on wetness. Northwest Africa was once lush but now is dry. Ramzi Touchan, of the University of Arizona in Tucson, and his colleagues have methodically looked at tree-ring data for a 500 year period. This geologic slice of information shows that droughts occur in irregular patterns. But the severest drought over that time span, as judged by the narrowness of the tree rings, was the recent period 1999-2002. This by itself does not prove that the Maghreb region of Africa is becoming more arid, says Touchan, but it does provide some baseline perspective from which to weigh later climate developments. (Results published in Geophysical Research Letters, August 2008)

Brown Carbon from China
Modeling the climate we already have and the climate we might be getting is an important task that depends crucially on the atmospheric factors researchers take into account, especially if they relate to materials that contribute to greenhouse warming by absorbing light. Usually these carbonaceous particles are understood to be minimally-absorbing organic carbon (arising from processes in nature) and light-absorbing black carbon coming from the burning of fossil fuels, usually during the generation of electricity or biomass combustion. The size, amount, and optical properties of this carbon are regularly incorporated into computer simulations of climate studies.
Scientists have now studied another type of carbon aerosol, one with a brown color. This species of carbon consists of spheres much larger (up to ten times larger) than ordinary soot and, the researchers believe, are formed not during the original act of combustion but in some later condensation of carbon in the sky. The new study looked at air samples over the Yellow Sea, next to China. Peter Crozier and his colleagues at the University of Arizona in Tucson argue that because these larger carbon spheres are rather abundant they need to be taken into account in future atmospheric warming models. The results were published in the August 8 issue of Science magazine.

Wind Dries the American West
Changes in wind patterns, most likely brought about by human activity, are making spring a drier and hotter time for the American Southwest. Scientists at of the University of Arizona in Tucson have scrutinized the tracks of spring storms for the twenty years between 1978 and1998 and notice that the storms tended to migrate northward over the years. This means that late-winter storms are bringing less precipitation. "We used to have this season from October to April where we had a chance for a storm," says Stephanie A. McAfee, one of the Arizona researchers. "Now it's from October to March."
The new research, published in an upcoming issue of the journal Geophysical Research Letters, correlates winter storm patterns with altering westerly winds, and this modification in turn is brought about by the influence of two human-related atmospheric conditions: increased greenhouse warming and the existence of an ozone-reduced zone (the “ozone hole”) over the poles. All of this tends to reduce the normal size of the snowpack and the subsequent flow of water in this arid part of the country.

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